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How to replace thermocouple (or thermopile), when burner must be removed
Caution: If you smell gas
Do NOT remove combustion door and expose gas to flame inside water heater
Leave house immediately.
Do not touch light switch on-or-off. Do not touch anything to cause static spark. Do not pick up phone. Call gas company from outside house.
NG natural gas is lighter than air and will rise to nose level, or can gather on ceiling
Propane LP gas is heavier than air and will hug floor.
Do not install LP propane heater below grade (in basement) or gas leak can fill basement will explosive gas.

Water heater safety precautions
Before spending money, check if pilot is ON
Pilot light is hard to see through sight glass.
Pilot flame is upward from sight glass.
Look into sight glass, and look upward.
Or use mirror to help look through sight glass so you do not have to sit on floor.
Flame should be clear blue.
Yellow flame indicates thermocouple is fine, but burner parts are dirty, vent is obstructed, or inadequate air supply, or dirty air intake
Before spending money, push in TCO
Newer models may have TCO located on front of combustion chamber
Temperature cut off will trip if temperatures inside combustion chamber exceed limit.
Wires on TCO are connected to gas control valve and prevent water heater from igniting.
Causes of tripped TCO include poor venting, dirty combustion parts, inadequate air supply to the water heater, clogged air intake

Thermal reset

Test ECO

Flammable vapor
SP20172 FV sensor reacts to gasoline vapors, shuts off gas control valve, and water heater will not work.
Pilot will not light .. replace sensor

FV sensor at Amazon
Flammable sensor kit

How flammable vapor sensor works
Flammable vapor .pdf

Lighted inspection mirror
Flame trap inspection mirror at Amazon
Before spending money, get some air
Do NOT underestimate need for adequate air and clean air intake. Save many $ up front right now.
1) Get more fresh air to water heater, especially in very hot location such as attic
2) Clean air intake so combustion can take place

Illustration on left applies to AO Smith, American, State, Reliance, Craftmaster, Kenmore, Whirlpool.
Other brands, and other models, might require removal of combustion parts to access arrestor screen.
Test thermocouple
How to test thermocouple
Test thermocouple and thermopile service manual/ pdf
How to troubleshoot gas water heater
How to install gas water heater
Bradford White Piezo igniter Test piezo igniter
The piezo igniter might not be giving spark to relight pilot?
Piezo igniter
Test piezo igniter
Hot surface igniter troubleshoot
How to light gas water heater
Thermocouple or thermopile?
Electronic gas control (top row on image) has thermopile if unit is not pilotless
Thermopile is several thermocouples together, so voltage produced by heat of pilot is large enough to power electronics inside gas control.
Test thermocouple
Test thermocouple and thermopile/ pdf

Mechanical gas control (lower row on image) has thermocouple
Troubleshoot by type of gas control
Thermocouple is 2 different metals with tip sitting in pilot flame. When heat is applied, small current is created that travels to gas control valve through copper tube.
If no electric signal is received as gas control valve, then small magnet closes off gas supply.
Thermopile is a cluster of thermocouples. More current is created, and current travels to gas control valve through small wire. The larger current is enough to power computer chip and error-code indicator light at the gas control valve. If no current is received, the chip closes off gas supply to gas control valve.
Steps start here
Gas water heater burner assembly
Door and burner assembly are removed to replace thermocouple
Larger image
Whole assembly is replaced
Newer models 2009- current (depending on brand and model)
Typical 6-year tank has 6 years parts and tank, so the part is covered 6 years, labor covered year 1.
Contact manufacturer with model number, serial number, to find exact part number and warranty coverage.
Water heater manufacturers
Age of water heater

Generic steps for replacing burner parts
Burner access door gasket
Some brands require separate door gasket.
Should have gasket on-hand in case removing door causes gasket to tear.
Some models
Gasket may be needed
Generally, water heaters from Rheem, Ruud, Richmond, GE, etc might require separate door gasket. Remove carefully if gasket is reused.

Water heaters from AO-Smith, American, State, Reliance, Kenmore, Whirlpool might have one-piece door and gasket that is reusable

Read product manual to identify parts.
If you do not have manual, look at label on side of water heater to identify company     Water heater manufacturers
General location of Thermocouple
Note: end of Thermocouple must sit in the pilot flame.
Heat from pilot creates small current that travels to gas control valve, and keeps control valve open so gas will flow to pilot and burner. If thermocouple falls away from pilot flame, or flame goes out, the absence of electric current will turn off gas to pilot and burner.

This type thermocouple requires removal of burner from combustion chamber
Step 1: Turn off gas
Locate gas shut off.
Handle parallel with gas line => Gas ON
Handle perpendicular across gas line => Gas OFF

Rotate gas shut off handle perpendicular across line to shut gas OFF.
Step 2: Notes before starting
Note each tube connected on bottom of gas control.
Note how tight each is when removing, so re-installation is about same.
a) Thermocouple connection is finger tight plus 1/4 turn
b) Manifold tube carries gas to burner
c) Pilot tube carries gas to pilot light
Gas has less psi than water, and connections do not need to be as tight.
Do not overtighten.

These connections do not need pipe sealant or teflon tape.

For propane, manifold tube threads are reverse.
Natural gas, threads are regular.
Step 3: Remove screws
Remove screws holding door

AO-Smith, American, State, Reliance, Kenmore, Whirlpool have hex screw
Rheem, Ruud, Richmond, GE have tamper-proof screws.
Use punch to break out center, and hex to remove

Manifold tab fits into bracket
Step 4: Remove burner
Be careful
Do not dump debris off the burner where it can fall down onto arrestor screen
Burner will hook into a slot, or slide out from under a holder, or slide out of a slot.
Refer to product manual for illustration.
AO Smith-American-State-Reliance-Kenmore-Whirlpool manuals generally have clear instructions and illustrations.
Do not expect Rheem-Ruud-Richmond-GE manual to have illustrations or instructions.

Manifold tab fits into slot, or bracket

DO not dump debris off burner
   Prevent clogging Step 5: Carefully vacuum out combustion chamber
Keep stuff from falling down onto the air intake screen
Step 6: Get ready to replace
Take photos
Mark-n-measure where new thermocouple should fit
End of Thermocouple must sit in pilot flame 3/8"-1/2" to work correctly
Pilot assembly will be held in location with screws
Step 7: Replace
Remove thermocouple by slowly, firmly pulling and twisting from bracket
If thermocouple will not disengage from pilot assembly, then replace entire assembly

Removal from door might be easier by cutting copper tube with wire cutter
Tip of thermocouple or thermopile is 3/8" to 1/2" into pilot flame
There will be a grommet-type holder to keep thermocouple in place.
Replace thermocouple pdf

Image shows 3-legged water heater
This type water heater is easiest to clean without removing combustion parts.
Step 7: Clean the air intake before putting parts back
Rheem, Ruud, Richmond, GE air intake screen located below combustion parts.
AO Smith, American, State, Reliance, Craftmaster, Kenmore, Whirlpool the air intake screen located  bottom of heater.
Use compressed air. Use borescope, or mirror and flashlight to inspect.
Clogged air intake screen will cause overheating.
Move boxes, rags, etc away from water heater for improved air flow
Slow incoming air supply, causes slower venting, yet same amount of gas is burned.
Slow venting with same amount of BTU output will overheat combustion chamber, and trip FV system.
Each manufacturer has different steps for repairing FV overheat, depending on Brand, Age, Model, etc of water heater.

Use soft brush, paint brush, compressed air, vacuum cleaner.
LP and NG models vary
Rule of thumb is .125" [or thickness of nickel]
Igniter and pilot must be positioned closely so gas escaping the pilot orifice will flow into hot ignitor.
Once the pilot ignites, the tip of thermocouple or thermopile must be in the pilot flame.

Larger image
Step 8: Re-install burner
Reinstall burner. Wait to reattach door screws until tubes are connected.
Re-connect tubes to gas control valve before attaching combustion door screws.
Manifold tube on LP gas water heater is reverse thread.
Do not overtighten tubes. Remember how tight each connection was when removing.
Thermocouple is finger tight + 1/4 turn.
If thermocouple is overtightened, the electric current produced by thermocouple will short out against gas control valve, and gas control will shut off gas to burner and pilot. Can result in damage to parts and water heater will not function and pilot will not stay lit.

Reinstall combustion door screws, with gasket properly aligned, and sealed
Step 9: Turn on gas
Turn on gas to water heater
Check all connections for gas leak using soapy water.
Use chloride-free soap and water
Propane is heavier than air, so smell close to floor
Natural gas is lighter than air, so smell higher
Give leak time to show itself, since gas pressure is lower than water pressure
Step 10: Light heater
Light gas water heater using instructions printed on side of water heater.
Gas flame should be clear blue, with small amount of yellow and some red.
Step 10: More Options
A) Call service technician to fix water heater

B) Continue troubleshooting:
How to troubleshoot gas water heater
How to repair Rheem FVIR

C) Install new water heater
How to install gas water heater
Recycle old water heater
Pilot flame troubleshoot Troubleshoot pilot flame
Tip of thermocouple or thermopile is 3/8" to 1/2" into pilot flame

It may be hard to see pilot flame on some models
Sight glass location varies by model of water heater
People often do not get low enough to see pilot flame.
When viewing pilot flame, generally you must look upwards through sight glass and to the right.
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